package cn.longhaul.test;

/**
 *  CRC16的校验算法工具类
 */
public class Crc16Util {

    /**
     * 一个字节包含位的数量 8
     */
    private static final int BITS_OF_BYTE = 8;
    /**
     * 多项式
     */
    private static final int POLYNOMIAL = 0x8408;
    /**
     * 初始值
     */
    private static final int INITIAL_VALUE = 0xFFFF;

    /**
     * CRC16 编码
     *
     * @param bytes 编码内容
     * @return 编码结果
     */
    public static int crc16(int[] bytes) {
        int res = INITIAL_VALUE;
        for (int data : bytes) {
            res = res ^ data;
            for (int i = 0; i < BITS_OF_BYTE; i++) {
                res = (res & 0x0001) == 1 ? (res >> 1) ^ POLYNOMIAL : res >> 1;
            }
        }
        return revert(res);
    }

    /**
     * 翻转16位的高八位和低八位字节
     *
     * @param src 翻转数字
     * @return 翻转结果
     */
    private static int revert(int src) {
        int lowByte = (src & 0xFF00) >> 8;
        int highByte = (src & 0x00FF) << 8;
        return lowByte | highByte;
    }


    /** 十六进制转为IntBytes
     * @param s 十六进制串
     * @return  int[] bytes
     */
    public static int[] hexString2IntBytes(String s) {
        int[] bytes;
        bytes = new int[s.length() / 2];
        for (int i = 0; i < bytes.length; i++) {

            bytes[i] = (int) Integer.parseInt(s.substring(2 * i, 2 * i + 2), 16);
        }
        return bytes;
    }

    public static void main(String[] args) throws Exception {
        int[] data = Crc16Util.hexString2IntBytes("18010206E28011700000020A7D001A0701000600000000");
        final int res = Crc16Util.crc16(data);
        final String hex = Integer.toHexString(res);
        System.out.print(hex);
    }

}
